SCIENTIFIC SURVEY. 



39 



posterior superior angle of the cranium and descending under the 

 neck, where it unites with the corresponding bone. Between 

 the rays of the fin and this bone, which resembles the scapula 

 (shoulder blade,) there is a range of small flat bones separated 

 by cartilaginous intervals, which may be compared to the bones 

 of the carpus. The rays of the ventral fins are articulated to 

 bones corresponding to the pelvis in the higher classes of ani- 

 mals. The pelvis is never articulated with the spine, nor does 

 it form an osseous girdle round the abdomen. 



In the Jugular and Thoracic fishes it is articulated to the base of the 

 osseous girdle which supports the pectoral fins. 



In the Abdominal fishes, the bones of the pelvis are never articu- 

 lated to the osseous girdle and are seldom connected with each 

 other. They are preserved in their situation by means of certain 

 ligaments. The rays of the caudal fin are articulated with the 

 last of the caudal vertebrae which is in general of a triangular 

 form and flat. 



The rays of the dorsal fin are supported by little bones, which have 

 the same directions as the spinous processes, and to which they 

 are attached by ligaments. 



As connected with the fins we may here take notice of those organs 

 which are termed cirri or ientacula (barbel which see) according 

 as they are placed about the mouth, or on the upper part of the 

 head. They are in general soft but often contain one jointed ray. 

 They do not differ in structure from the fins, and are so closely 

 connected with them, that it is diflicult to point out their use. 



The motions of a fish are performed by means of its fins. The 

 caudal is the principal organ of progression. Those fins which 

 are situate on the back are termed Dorsal. These vary greatly 

 in shape and number. 



Fig. 1. 



a. First dorsal. 



b. Second dorsal. 



c. Caudal. 



d. Anal. 



e. Ventral. 



T a _&-*^ f- Pectoral. 



d e -^-^ 



The fin which surrounds the extremity of the tail is termed Caudal 

 fin, and is always placed perpendicularly. It is forked in some 



